Alkaline detergent



' employed.

Patented Dec. 1, 1942 2.303.398 ALKALINE DETERGENT Eharles Schwartz, Pittsburgh, Pa... assignor to Hall Laboratories, Inc., Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Application May 1, 1939,

Serial No. 211,177

9 Claims. (01. 252-135) This invention relates generally to alkaline preparations, for example alkaline detergents for cleaning soft metals and more particularly to such detergents containing an inhibiting agent for preventing the alkaline corrosion of the metal.

It is a well known fact that many highly alkaline detergents while performing excellently as cleaners can not be used for the cleaning of soft metals such as aluminum and tin, since the alkalies corrode and dissolve the metals quite readily.

Many efforts have been made to utilize the ex-- cellent detergent properties of highly alkaline mixtures and at the-same time to prevent, in so far as possible, the attack upon soft metals. Thus the use of certain silicates has been successful in decreasing to a considerable extent the corrosion of aluminum in alkaline solutions. It is necessary, however, to be very careful in the choice of silicate used and in the concentration of the solution in order to avoid very serious attack upon the metal being washed. If the concentration of the solution is too high or too low, it attacks the aluminum and this places a serious limitation on the typeof solution which may be silicates have been used also for cleaning tin but in this case the alkalinity of the cleaning solution must be adjusted to so low apH and the temperature of cleaner dropped to such an extent that effective cleaning can not easily be obtained. Other remedies for the corrosion of tin and aluminum by alkaline cleaners have been suggested also. In the case of tin, the use of sodium sulphite has become quite widespread in recent years. This material decreases the oxygen concentration of the cleaning solution and in hibits the corrosion of tin by alkalies. However, there is considerable corrosion after the sulphite is depleted, as it is very shortly in usual practice. Where the solution is heated in contact with air, the sodium sulphite is readily converted into as "chromic ulcersfiiwhich necessitate cessation of all work with material containing chromates and which require long periods of time for healing.

It is an object of the present invention to provide means by which alkaline detergents may be made safe for cleaning soft metals. The present invention has many advantages over the methods previously employed. Aluminum, tin, zinc, lead,

cadmium or other soft metals or alloys thereof l may be treated with solutions of extremely high pH at boiling temperatures for long periods of time without showing any evidence of corrosion. The cleaning solutions preferably have a pH of at least 10 and in many cases the pH is as high as 12 or over. The corrosion inhibitors which I employ do not decrease in effectiveness with time, as do the sulphites, but remain effective over long periods. They are without harmful eflect upon the human skin and will not occasion the diiiiculties accompanying the use of chromates or dichromates. I

I have found that the salts of mercury, either the mercurous salts or the mercuric salts, when added in proper proportion to alkalies prevent entirely the characteristic corroding efiect of the tin even at relatively low temperature.

alkalies on the soft metals. Although some of the mercurous salts, as for example mercurous chloride, are generally insoluble in water, they are nevertheless operative in inhibiting corrosion under the condition hereinafter described. I believe that this is due to what may be called an "auto-oxidation-reduction reaction in which part of the mercury in the mercurous chloride is reduced to metallic mercury and the remainder is oxidized to the mercuric state, this latter portion acting as the corrosion inhibitor. Although I have not as yet definitely proved this happens, it is nevertheless a fact that mercurous chloride acts as an inhibitor in the presence of alkalies and that there is a precipitation of what appears to be metallic mercury in the solution. The mechanism whereby the corrosion is prevented is unknown but it probably can be ascribed to the formation of nonreactive protective films on the metal surfaces.

Sodium metasilicate, sesquisilicate and orthosilicate are strong alkalies, their alkalinity in creasing in the order listed. It is well known that even the weakest of these, namely sodium metasilicate when used for example to wash tin or tin plate causes rapid spangling and solution of the I have found that by adding a small quantity of a mercury salt to any of these silicates the corrosive effect of the solution subsequently made from it is reduced to zero evenat boiling temperatures over long periods of time.

The following Tables I, II and III, forexample, indicate the results that have been obtained when several pieces of tin plate were heated in alkaline solutions at 60 C. for the periods of time specified. The results show the per cent lossfin weight of the tin in the cases where the alkali did not contain any mercury salt and in the cases where it did contain a mercury salt as an inhibite Mercuric-chloride was used in these ing agent. tests as a typical mercury salt.

In Table I, the alkaline solution was a 0.5% aqueous solution of sodium metasilicate aloneand also with 5% of mercuric chloride based on phate and sodium metasilicate.

Table I (Per cent loss in weight) 0.5% aqueous solution of sodium metasilicate+5% mercuric chloride (based on weight of sodium metasilicate) 0.5% aqueous solution of sodium metasilicate Hours Table II (Per cent loss in weight) loss in weight of .803% after heating for 222 hours. The mercury salts exhibit similar inhibiting effect, when they are used with trisodium ortho- 5 phosphate alone as shown in Table II or with mixtures of sodium meta'silicate and trisodium orthophosphate as shown in Table 111.

While mercuric chloride has been referred to r in the examples as a typical mercury salt which of'n-hibits the corrosion of soft metals; I may emloy other mercury salts, either mercurous or *mercuric-saltsFThe mercury salts which are effective as corrosion inhibitors according to the present invention'are those which are water-soluble orwhic'h when placed in the alkaline solu- "tion to be used'in cleaning the soft metal undergo a reaction which solubilizes an appreciable proportion of themercury. These salts are referred to herein-after assolulile mercury salts. I may use thesoluble mercurous or mercuric salts, such as the chlorides, nitrates, acetates, .salic in fact any other soluble mercurysalt.

Ordinarily the mercury salt should be used in. an amount equal to at least 1%,,based {on the weight of the alkali present and generallyin an amount-of at least 2% by, weight. 'When the cleaning solution is used at low temperatures, it is possible to decrease the amount of mercury salt evenbelowthe lowestfigurepreviously given. Generally it is unnecessary to use more than of the mercury salt, although more might be used without harmful effect. I:

The detergent solution containing the corrosion inhibitor is useful in'all cases where ahighly alkaline detergent is required. Itmay be used for example in the ,,washing,of. tin plate, tubes,

bakery" pans, milk cans, and .in tinfabricatlng plants. In the fabrication of tin plate, or arti-"- cles made therefrom, it is often necessary toapply grease] to aid in the forming operations.

This may be removed by the use of a highly alkaline cleaning solution in accordance with the present invention without attack on the tin. The cleaningsolutions maybe used also in the treatment of aluminum, In this case also, the solution may be used to remove the grease employed in fabricating the aluminum without, however, causing alkaline corrosion of the aluminum.

0.5% aqueous solution of tri- For washing pans in a bakery where the pans Hours ii i t ri l d i i ggfggg gg gg gggggggf gggg are washed fairly frequently, so that theamount Phmhm oltrisodium phosphate) of burned on matter is not excessive, I may use p a cleaning composition containing about 95% 9. .194 0.0124 sodium metasilicate and 5% of mercuric chloride ggggjg: 335; or other soluble mercury salt. This is dissolved in water to form a solution of astrength between of 1% and 3%, generally in the neighborhood Ta I of a 1%,solution', In cleaning the bakery pans, (Per cent loss in weight) they might be boiled in the cleaning solution for an hour. aqueous solution of a mi Where thedeposits on the bakery pans are exol z sgu f of 40% Osmium cess1ve, I might use an aqueous solution of a mmmsodium ph p a and spdium composition containing 95% sodiumorthosilicate Hours orthonhosphate metas1licate+5% mercuncchloride (based on weight of trisodium orthophosphate and sodium metasilicate) and 60% sodium metasilicatc hours tin the sodium metasilicate solution. In

the absence of the mercury salt, there was-a 75 and 5% mercuric chloride or other soluble mercury salt and boil the pans for an hour in that solution. This providesv a more alkaline solution than in the case just mentioned.

As another example, I might use a 1% aqueous solution of a composition containing 60% sodium metasilicate, 35% sodium hydroxide and 5% mer curic chloride or other soluble mercury salt where a highly alkaline solution is desired". I might add to this composition or to any of the compositions a wetting agent, such as a sodium salt of a sulphated' fatty alcohol in the amount of 13% based on the total weight of the solids.

ylates or The soluble mercury salts also act as inhibitors of corrosion in the presence of mixtures of alkalies with soap, casein, defiocculating agents, wetting agents, abrasives and the like.

The soluble mercury salts effectively inhibit the corrosion of tin, aluminum and other soft metals by alkali-metal carbonate solutions as well as solutions of the alkali-metal phosphates and silicates. I may add sodium hydroxide or other alkali to the silicates, phosphates or carbonates in any case where it is desired to increase the alkalinity and the corrosion of the metal may be inhibited by the use of soluble mercury salts.

The invention enables the use of highly alkaline solutions in the cleaning of soft metals without corrosion of the metal. Although the invention has been described particularly in connection with preventing the corrosion of aluminum and tin, it is applicable also to the treatment of zinc, lead,

cadmium or other soft metals or alloys thereof. The term soft metal as used here is intended to include any metal or alloy which under the proper conditions of temperature and concentration tends to beattacked or dissolved by alkaline solutions.

Although the principal use of the invention is in connection with cleaning solutions, the invention is applicable to inhibiting corrosion of alkaline compositions in general, such for example as paints or adhesives. The addition of a soluble mercury salt to an alkaline paint or adhesive will prevent the attack of the paint or adhesive on soft metals, during the time required for the paint or adhesive to set or harden.

The invention is not limited to the examples, which have been given merely for illustrative purposes, or to the preferred proportions, but may be otherwise embodied or practiced within the scope of the following claims.

I claim:

1. An alkaline detergent composition for soft metal, comprising an alkali-metal salt of the group consisting of silicate, phosphate and carbonate, said detergent composition having a pH of at least 10 in aqueous solution and which under normal conditions of use will corrode the soft metal, said detergent composition comprising at least about 1% of a mercury salt based on the weight of said alkali-metal salt to inhibit corrosion of the soft metal, said mercury salt being soluble in the aqueous solution of said alkali-metal salt.

2. An alkaline detergent composition for soft metal, comprising an alkali-metal silicate, said detergent composition having a pH of at least 10 in aqueous solution and which under normal conditions of use will corrode the soft metal, said detergent composition comprising at least about 1% of a mercury salt based on the weight of said alkali-metal silicate to inhibit corrosion of the soft metal, said mercury salt being soluble in the aqueous solution of said alkali-metal silicate.

3. An alkaline detergent composition for soft metal, said detergent composition comprising by weight about 60 to 95% sodium metasilicate, an effective amount up to about 35% sodium hydroxide and about 1 to 10% of a mercury salt, said mercury salt being soluble in the aqueous solution of said sodium metasilicate.

4. An alkaline detergent composition for soft metal, said detergent composition comprising by weight about 95% sodium metasilicate and about 5% of a mercury salt, said mercury salt being soluble in the aqueous solution of said sodium metasilicate.

5. An alkaline detergent composition for soft metal, said detergent composition comprising by weight about 95% sodium metasilicate and about 5% mercuric chloride.

6. An alkaline detergent composition for soft metal, said detergent composition comprising by weight about 95% sodium orthosilicate and about 5% of a mercury salt, said mercury salt being soluble in the aqueous solution of said sodium orthosilicate.

7. An alkaline detergent for soft metal, said detergent composition comprising by weight about 95% sodium orthosilicate and about 5% CERTIFICATE CHARLES It is hereby certified that error of the above 0nd column, an that the in that the fice.

Signed and sealed this 19th day (Seal) mercuric chloride.

8. An alkaline detergent composition for soft metal, said detergent composition comprising by weight about sodium metasilicate, about 35% sodium hydroxide and about 5% mercuric chloride.

9. An alkaline detergent composition for soft metal, said detergent composition comprising by weight about 60 to sodium metasilicate, an effective amount up to about 35% sodium hydroxide and about 1 to 10% mercuric chloride.

CHARLES SCHWARTZ.

or CORRECTION.

I December 1, 1914.2.

SCHWARTZ.

appears in the printed specification numbered patent requiring correction as follows: Page 5, secline 56,, claim 7, after detergent insert -composition--; said Letters Patent should be read with this correction theresame may conform to the record of the case in the Patent Of'- of January, A. D. 1915.

Henry Van Arsdale Acting Commissioner of Patents.

CERTIFICATE oF CORRECTION. Patent No. 2,505,598. A December 1, 19 42.

' ems SCHWARTZ.

, It is hereby certified that error appeers in the printed Specification of the above numbered patent requiring correction as follows: Page 5, second column, line 56, claim 7, after "detergent" insert --COmPOS1t10n--; eni that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case ,in the Patent Of-- fice.

Signed and sealed this 19th day of January, A. I). 1911.}.

Henry Van Arsdale;

(Seal) 7 Acting Commissioner of Patents. 

